450 



NA TURE 



\Sept. 8, 1 88 1 



M. du Trembley twenty-five years ago, the ether would be 

 vaporised, and we should be able to start afresh with high ten- 

 sion vai-our, which in its turn would be expanded until the 

 frictional limit was again reached. At that point the ether 

 would have to be condensed by the outward application of cold 

 water and pumped back, in the liquid .'tate, to act over again in 

 a similar manner. This method of working was extent ivcly 

 tried in France w hen introduced by M. du Trembley, and the 

 results were sufficiently encouraging to justify a resumption of 

 the trials at the present time, when they could be made under 

 much mure favourable conditions. There was no questicm as lo 

 the economy effected, but in the discussions which took place on 

 the subject it was contended that equally good results might be 

 attained by improved applicatic ns of the steam, without resort- 

 ing to an additional medium. The compound engine of the 

 present day does in fact equal the efficiency of Du Trembley's 

 combined ^team- and ether-engine, but there is no reason wliy 

 the ether apparatus should not confer the same advantage on 

 the modern engine tliat attended its application to the older 

 form. The olijections to its use are purely of a practical nature, 

 and might very possibly yield to per?evering efforts at removal. 



I need scarcely notice the advantage to be derived from in- 

 creasing the initial pressure of the tteam so as to widen the 

 range of expansion by raising the upper limit of temperature 

 instead of reducing the lower one. It nmst be remembered 

 ho^^ ever that an increase of temperature is attended w ith the 

 serious drawback of increasing the quantity of heat carried off 

 by the gases from the fire, and also tlie loss by radiation, so that 

 we have not so much to gain by increaie of pressure as is 

 commonly imagined. 



But even supposing the steam-engine to te improved to the 

 utmost extent that practical considerations give us reason to 

 hope for, we should still have to adjudge it a wasteful thougli a 

 valuable ervant. Nor does there appear to be any prospect of 

 substituting with advantage any other form of thermodynamic 

 engine, and thus we are led to inquire whether any oiher kind 

 of energy is likely to serve us better than heat, for motive power. 



Most people, especially those who are least competent to 

 judge, look to electricity as the coming panacea for all mecha- 

 nical deficiency, and certainly the astonishing progress of electri- 

 city as applied to telegraphy, and to those marvellous instru- 

 ments of recent invention which the British Pest Office claims to 

 include in its monopoly of the electric telegraph, as well as the 

 wonderful advance w hich electricity has made as an illuminating 

 agent, does tend to impress us with faith in its future greatness 

 in the realm of motive power as well. 



The difference between heat and electricity in their modes of 

 mechanical action is very wide. Heat acts by expansion of 

 volume which we know to be a neces-arily wasteful principle, 

 while electricity operates by attraction and repulsion, and thus 

 produces motion in a manner which is subject to no greater lo>s 

 of effect than attends the motive action of gravity as exemplified 

 in the ponderable application of falling water in hydraulic 

 machines. If then we could produce electricity with the ; ame 

 facility and economy as heat, the gain would be enormou-, but 

 this, as yet at least, we cannot do. At present by far the 

 cheapest method of generating electricity is by the dynamic 

 process. Instead of beginning with electricity to produce 

 power, we begin with power to produce electricity. As a 

 secondary motor an electric engine may, and assuredly will, 

 play an important part in future applications of power, liut ouj- 

 present inquiry relates to a primary, and not a secondary, em- 

 ployment of electricity. Thus we are brought to the question. 

 From what source, other than mechanical action, can we hope 

 to obtain a supply of electricity sufficiently cheap and abundant 

 to enable it to take the place of heat as a motive energy ? It is 

 commonly said that we know so little of the nature of electricity 

 that it is impossible to .'Ct bounds to the means of obtaining il ; 

 but ignorance is at least as liable to mislead in the direction of 

 exaggerated expectation as in that of incredulity. It may be 

 freely .admitted that the nature of electricity is much less under- 

 stood than that of heat, but we know that the two are very 

 nearly allied. The doctrine that heat consi-ts of internal motion 

 of molecules may be accepted with almost absolute certainty of 

 its truth. The old idea of heat being a separate entity is no 

 longer held except by those who prefer the fallacious evidence 

 of their senses to the demonstrations of science. So also the 

 old idea of electricity having a separate existence from tangible 

 matter must be discarded, and we are justified in concluding that 

 it is merely a strained or tensional condition of the molecules of 



matter. Although electricity is more prone to pass into heat 

 than heat into electricity, yet we know that they are mutually 

 convertible. In short I need scarcely remind you, that accord- 

 ing to that magnificent generaliation of modern limes, so preg- 

 nant with great consequences, and fcr wh'ch we are indebted to 

 many illustrious investigs.tors, we now know that heat, elec- 

 tricity, and mechanical action, are all equivalent and transposable 

 forms of energy, of w hich motion is the essence. 



To take a cur. ory view of r-ur available sources of energy, we 

 have, firstly, the direct heating pow er of the sun's rays, which as 

 yet we have not succeeded in api-lying to motive purposes. 

 Secondly we have water power, wind power, and tidal power, 

 all depending upon influerces lying outside of our planet. .\nd 

 thirdly we have chemical attraction or affinity. ISeyond these 

 there is nothing worth naming. Of the radiant heat of the sun 

 I shall have to sptak hereafter, and bearing in mind that we are 

 in search of electricity as a cause, and not an effect, of motive 

 pow er we may pass over the dynamical agencies comprised under 

 the second head, and ilirect our attention to chemical affinity as 

 the sole remaining source of energy availalde for our purpose. 

 At present we derive motive power from chemical attraction 

 through the medium of heat only, and the question i', can we 

 with advantage draw upon the same source through the medium 

 of electricity. The process by which we obtain our supply of 

 heat from the exercise of affinity is that of combustion, in which 

 the substances used consist, on the one hand, of those we call 

 fuel, of which coal is the most important, and on the other, of 

 oxygen, which we derive from the atmosphere. The oxygen has 

 an immense advantage over every other available substance in 

 being omni| resent and co-tless. The only money value involved 

 is that of the fuel, and in u'-ing coal we empiloy the cheapest 

 oxidisable substance to be found in na'ure. Moreover the weight 

 of coal used in the combination is only about one-third of the 

 weight of oxygen, so that we only pay upon one-fourth of the 

 w hole material consumed. Thus we have conditions of the most 

 favourable description for the production of energy, in the form 

 of heat, and if we c uld only use the affinities f.f the san.e sub- 

 stances w ith equal facility to evolve electric energy instead of heat 

 energy, there would he nothing more to desire ; but as yet there 

 is no appearance of our being able to do this. According to 

 our present practice we consume zinc, instead of coal, in the 

 V Itaic production of electricity, and not only is zinc thirty or 

 forty times dearer than coal, but it requires to be used in about 

 six-fold larger quantity in order to develop an equal amount of 

 energy. Some people are bild enough to say that with our 

 present imperfect knowledge of electricity we have no right to 

 condemn all plentiful substance:, other than coal, as impracti- 

 cable substitutes for metallic zinc, but it is manifett that we can- 

 not get energy from affinity, where affinity has already been 

 satisfied. The numerous bodies which constitute the mass of 

 our globe, and which we call earths, are bodies in this inert 

 condition. They have already, by the union of the two ele- 

 ments composing them, evolved the energy due to combination, 

 and that energy has ages ago been dissipated in space m the 

 form of heat, never again to be available to us. As well might 

 we try to make fire with ashes, as to use snch bodies over aga'n 

 as sources of either heat or electricity. To make them fit for 

 our purpc'se we should first have to annul their ^tate of combi- 

 nation, and this would require the expenditure of more ( nergy 

 upon them than we could derive from their rccoml inntion. 

 Water, being oxidised hydrogen, irust be placed in the same 

 category as the earths. In short the only abundant substances 

 in nature possessing strong unsatisfied ..ffinities are those of 

 organic origin, and in the absence of coal, which is the accumu- 

 tated product of a past vegetation, our supply of such sul stances 

 would be insignificant. This being the case, until a means be 

 found of making the comliination of coal with oxygen directly 

 available for the development of electric energy, as it now is of 

 heat energy, there seems to be no probability of our obtahiing 

 electricity from chemical action at such a cost as to supplant 

 heat as a m^.tive agent. 



But while still looking to heat ns the fountain-head of cur 

 power, we may very possibly learn to transmute it, eci nrm-cally, 

 into the more available form of electricity. One method of 

 transformation we already possess, and we have every reason to 

 believe there are others yet to be discovered. We know that 

 when dissimilar n etals sre joined at opposite ends, and heated 

 at one set of junctions while they are cooled at the other, part of 

 the heat applied disappears in the process, and assumes the form 

 of an electric current. Each couple of metals may be treated as 



